Portugal defeated Guatemala 1-0 on Tuesday to set up a quarterfinal against Argentina at the Under-20 World Cup.
Nelson Oliveira's 7th-minute penalty gave Portugal an early lead that it maintained throughout the match.
Portugal reached the knock-out stage by topping its group with two victories and a draw. Guatemala won its last group match 1-0 against Croatia and entered as one of the top third-place teams.
Portugal next plays six-time champion Argentina, which defeated Egypt 2-1 on Tuesday in Medellin.
''I have some bittersweet feeling for advancing to the quarterfinals this way,'' said Portugal coach Ilidio Vale, suggesting his team had underestimated the Central Americans. ''I'm convinced the next game will be different. We have to be more competitive.''
Portugal had 65 percent of possession in the first half and had the better chances against Guatemala.
The Portuguese were also dominant early in the second half as well but failed to finish off their scoring opportunities. As the half wore on, however, Guatemala began to create openings and probably deserved to equalize.
Jose Melgar had a great chance in the 70th, but his long-range shot was just wide of the far post and Portuguese keeper Mika. Elias Vasquez also just missed in the 77th, his shot inches outside the post to Mika's right. Mika also stopped a point-blank shot in the 84th with Guatemala pressing.
Kevin Norales hit the post in the 88th on a 30-meter (yard) free kick, with Guatemala again coming close.
''This was a team that did not want to lose,'' said Guatemala coach Ever Almeida, who was critical of the refereeing. ''We didn't make it for various reasons.''
